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There have been known various classifications of landslides. Broad definitions include forms of mass movement that narrower definitions exclude. For example, the McGraw-Hill Encyclopedia of Science and Technology distinguishes the following types of landslides:
- fall (by undercutting)
- fall (by toppling)
- slump
- rockslide
- earthflow
- sinkholes, mountain side
- rockslide that develops into rock avalanche
Influential narrower definitions restrict landslides to slumps and translational slides in rock and regolith, not involving fluidisation. This excludes falls, topples, lateral spreads, and mass flows from the definition.[1][2]
The causes of landslides are usually related to instabilities in slopes. It is usually possible to identify one or more landslide causes and one landslide trigger. The difference between these two concepts is subtle but important. The landslide causes are the reasons that a landslide occurred in that location and at that time and may be considered to be factors that made the slope vulnerable to failure, that predispose the slope to becoming unstable. The trigger is the single event that finally initiated the landslide. Thus, causes combine to make a slope vulnerable to failure, and the trigger finally initiates the movement. Landslides can have many causes but can only have one trigger. Usually, it is relatively easy to determine the trigger after the landslide has occurred (although it is generally very difficult to determine the exact nature of landslide triggers ahead of a movement event).
- ^ Varnes D. J., Slope movement types and processes. In: Schuster R. L. & Krizek R. J. Ed., Landslides, analysis and control. Transportation Research Board Sp. Rep. No. 176, Nat. Acad. oi Sciences, pp. 11–33, 1978.
- ^ Hungr O, Evans SG, Bovis M, and Hutchinson JN (2001) Review of the classification of landslides of the flow type. Environmental and Engineering Geoscience VII, 221-238.